Glass laminated products, such as safety glass, have contributed to society for almost a century. Safety glass also found uses in structural, decorative or other architectural applications.
Safety glass typically consists of a sandwich of two glass sheets or panels bonded together with a polymeric interlayer of a polymeric sheet. One or both of the glass sheets may be replaced with optically clear rigid polymeric sheets, such as sheets of polycarbonate materials. Safety glass has further evolved to include multiple layers of glass and/or rigid polymeric sheets bonded together with interlayers.
The interlayer is typically made with a relatively thick polymer sheet, which exhibits toughness and bondability to provide adhesion to the glass in the event of a crack or crash. Widely used interlayer materials include complex, multicomponent compositions based on poly(vinyl butyral) (PVB), poly(urethane) (PU), poly(ethylene-co-vinyl acetate) (EVA), and the like.
As a renewable energy resource, the use of solar cell modules is rapidly expanding. One preferred way of manufacturing a solar cell module involves forming a pre-lamination assembly comprising at least 5 structural layers. The solar cell pre-lamination assemblies are constructed in the following order starting from the top, or incident layer (that is, the layer first contacted by light) and continuing to the backing layer (the layer furthest removed from the incident layer): (1) incident layer (typically a glass plate or a thin polymeric film (such as a fluoropolymer or polyester film), but could conceivably be any material that is transparent to sunlight), (2) front encapsulant layer, (3) solar cell component, (4) back encapsulant layer, and (5) backing layer.
The encapsulant layers are designed to encapsulate and protect the fragile solar cell component. Generally, a solar cell pre-lamination assembly incorporates at least two encapsulant layers sandwiched around the solar cell component. The optical properties of the front encapsulant layer may be such that light can be effectively transmitted to the solar cell component. Additionally, encapsulant layers generally have similar requirements and compositions to that described above for safety glass interlayers.
The use of acid copolymers of α-olefins and α,β-ethylenically unsaturated carboxylic acids in forming safety glass interlayers has been known within the art (see, e.g., U.S. Pat. No. 3,762,988). The use of such acid copolymers in forming solar cell encapsulant layers has been disclosed in, e.g., U.S. Pat. Nos. 5,508,205; 6,187,448; 6,320,116; 6,414,236; 6,586,271; 6,693,237; and 6,777,610, U.S. Pat Appl Nos. 2004/0191422 and 2006/0207645; European Pat No. 1 544 921; Japanese Pat Nos. JP 2000186114; JP 2001089616; JP 2001119047; JP 2001119056; JP 2001119057; JP 2001144313; JP 2001261904; JP 2001332751; and JP 2002335005; JP 2004031445; JP 2004058583; JP 2006032308; JP 2006036875; and JP 2006190867, and PCT Pat Appl No. WO 03/041177).
Acid terpolymers of α-olefins, α,β-ethylenically unsaturated carboxylic acids, and α,β-ethylenically unsaturated carboxylic acid esters have also been used in forming safety glass interlayers (see e.g., U.S. Pat Appl No. 2001/0008695) or solar cell encapsulant layers (see e.g., U.S. Pat. Nos. 3,957,537 and 6,414,236, and Japanese Pat Nos. JP 2004031445 and JP 2004058583).
However, safety glass interlayers and solar encapsulant layers formed of such acid copolymers tend not to have adequate light transmission properties and sufficient adhesion strength to other laminate layers, especially under severe environmental testing. Moreover, the solar cell encapsulant layers formed of such acid copolymers often fail to provide adequate protection to the solar cell component from shock. On the other hand, safety glass interlayers and solar encapsulant layers formed of the acid terpolymers taught by the prior art also do not have the desired light transmission property and adhesion strength to other laminate layers. In addition, less heat resistance is often associated with the glass interlayers or solar cell encapsulant layers derived from such acid terpolymers, due to their low melting points. One way to overcome this is to add organic peroxides to the acid terpolymer compositions. However, the addition of organic peroxides may complicate the melt compounding, the sheet formation, and/or the lamination process. For example, when such acid terpolymer compositions are used in forming the solar cell encapsulant layers, it is necessary to use a two-step lamination process to prepare such solar cell laminates. Particularly, after a pre-lamination assembly is assembled, it is necessary to have a low temperature step to allow the encapsulant film or sheet layer to adhere to the other laminate layers and a high temperature step to cure the films or sheets to provide the enhanced thermal resistance.
There is a need for polymeric films or sheets suitable as safety glass interlayers or solar cell encapsulant layers, which are transparent, highly adhesive to other laminate layers, and moisture and heat resistant.